This invention relates to thin-film magnetic transducers of the type used to write data to and/or read data from magnetic discs.
Thin-film magnetic transducers are used widely within the computer industry for writing data to, and reading data from, magnetic media. In a typical data storage and retrieval system, a controller and actuator place the transducer adjacent a moving magnetic medium such as a rotating disc. The transducer writes data to the medium by imparting a magnetic field to the medium and reads data from the media by sensing the magnetic field from the medium as it passes the transducer.
Thin-film magnetic transducers typically comprise two opposing magnetically-permeable layers or films, called pole pieces, a transducing gap, and an inductive coil. The pole pieces, usually a top and a bottom pole piece, are spaced apart to form the transducing gap and are connected at a junction distal from the transducing gap. The inductive coil is an insulated conductor wound around one or both of the poles to achieve a magnetic linkage.
To write a data pattern, an electric current is supplied to the inductive coil to induce a magnetic flux to circulate from one pole, across the gap, into the other pole. The flux crossing the gap impresses a magnetic field onto a surface of a magnetic disc rotating adjacent the gap. The magnetic field coerces magnetic domains on the disc into alignment with the magnetic field, leaving a recoverable magnetic data pattern. Reading such a pattern entails moving the gap adjacent the pattern on the rotating disc. The magnetic pattern imposes a changing magnetic field on the gap and the top and bottom poles, creating a changing flux in the poles. This flux in turn induces an electric signal in the inductive coil. Electric circuitry connected to the coil ultimately translates the signal into a retrieved data pattern.
Thin-film magnetic transducers are often fabricated by a photolithographic process. The process entails depositing successive layers of conductive, magnetic, and insulating material onto a substrate using photoresists, photomasks, and chemical etchants to define specific patterns for the magnetic poles, inductive coil, insulated gap, and other portions of the transducer.
One problem inherent to thin-film magnetic transducers is flux shunting. Flux shunting refers to the behavior of magnetic flux in a two-pole magnetic circuit where flux traveling in one pole jumps to the other pole before traveling the complete circuit. Generally, a two-pole magnetic circuit consists of a front gap, and two parallel poles joined at a distal back-gap junction. The two poles, composed of magnetic material, are typically stacked, one atop the other, in close proximity., with a layer of insulating material between them. Ideally, flux would circulate through the magnetic circuit along one pole, across the distal back-gap junction, and along the second pole back to the front gap. In practice, however, some flux shunts, or leaks, directly through the insulating layer from one pole to the other rather than following the defined magnetic circuit. This shunted, or leakage, flux contributes only partially to the magnetic coupling between the poles and the inductive coil. Flux shunting, therefore, diminishes transducer efficiency by reducing both voltage sensed during reading and flux induced during writing.
Analytically, flux shunting may be likened to a partial short circuiting in electric circuits where the amount of short circuiting depends on the resistance between the conductors. Similarly, flux shunting depends on the magnetic resistance, or reluctance, of the insulating material between two magnetic conductors or pole pieces. The amount or degree of flux shunting is inversely proportional to the reluctance of the insulating material. In general, reluctance varies directly with the length and permeability of the insulating material and inversely with its cross-sectional area. Thus, the amount of flux shunting between two poles of a transducer is-fixed by the dimensions and composition of an interior insulated region bounded by the two poles, the transducing gap, and the distal back-gap junction. Accordingly, the problem of flux shunting has been addressed by introducing a bow into one or both poles to increase the thickness of the insulating layer and the distance between the poles. Introducing the bow requires building a "hill" of insulation layers ascending away from the front gap and descending toward the back-gap junction. Insulating layers forming the hill, however, are usually applied by a spin process, which is difficult to control at the increased heights needed for the bow. Thus, fabricating the bow increases the complexity and cost of manufacturing the poles. Moreover, the tendency of magnetic flux to fringe near discontinuities, such as a bow, limits the degree to which the pole may be bowed without compromising the effectiveness (flux channeling efficiency) of the magnetic circuit.
Another problem of prior magnetic pole structures concerns the inductive coil. Typically, the coil is wound into a flat spiral around the back-gap junction of the poles, dividing the coil into front and rear halves. The front half, therefore, lies sandwiched between the poles, and the rear half lies behind the back-gap junction. Only the sandwiched, front half of the coil magnetically links to the poles. The "unsandwiched" rear merely completes the electric circuit of the coil. In other words, it adds nothing to the magnetic coupling between the coil and the poles. In fact, the electrical resistance of the unsandwiched portion detracts from the overall efficiency and performance of the magnetic transducer.